Liquid dispenser systems, such as liquid soap and sanitizer dispensers, provide a user with a predetermined amount of liquid upon actuation of the dispenser. In addition, it is sometimes desirable to dispense the liquid in the form of foam by, for example, injecting air into the liquid to create a foamy mixture of liquid and air bubbles by use of an air pump or air compressor. Many liquid and foam dispensers use non-collapsing containers. Non-collapsing containers must be vented when fluid is pumped out of the container or the container will collapse and/or prevent the pump from dispensing the fluid. When the non-collapsing containers are used in an inverted position with the pump located at the bottom of the container, prior art vent valves tend to leak or have a high cracking pressure to prevent leaking, which causes collapsing or partial collapsing of thin containers.
Depending on the type of material the container is made of, certain non-collapsing containers, such as those made from PET, are very sensitive to thickness for collapsing. Accordingly, if the valve has a high cracking pressure, the container either collapses/partially collapses or has to be made with thick walls. In addition, vent valves with higher cracking pressure may cause inconsistent product output. Collapsed or partially collapsed containers are less aesthetically pleasing and containers with thicker walls are not environmentally friendly.